There are 6 levels in all, and they are all challenging. If you lose even once, you lose the game and have to start over.
Toad was bored so he took a walk and looked around for something to do. The first thing he saw was that the Dark Mr. I had broken out of The Dark Dimension and was attempting to take over the world. He cast a spell that would put it back, which would take 14 seconds. During those 14 seconds, he had fun dodging all of the attacks from the Dark Mr. I.
The way the the Dark Mr. I's escape worked was it opened a barrier between the Dark Dimension and the real world, so you could just walk between them. This is why you can see the Dark Dimension in the game. Also, it was shooting into the real world. All the attacks aimed at toad and he dodged, hit somebody else and they died. They will not be missed, since nobody knows who was shot, since the Dark Mr. I's attacks erase whatever they hit from the timeline so no one remembers them.
Then a bunch of Toadlebugs started falling out of the sky, and so Toad caught all of them as a challenge.
Then he got the Toad Snow to act like a Dance Dance Revolution game, and then he went around avoiding other enemies, going on adventures setting other pointless challenges for himself, like dodging Tetris blocks in Tetris Hell, and bouncing a Toadguy on his head for several seconds trying to teach it how to fly (which it already could).
The following characters appear in Toad's Fun Releasio Adventure: